A Tower With an Improved Posture

More than 11 years after it was condemned as unsafe, the Leaning Tower of Pisa will soon reopen to a public eager to climb it--an experience as unsettling as a walk on a ship’s deck in a swelling sea.

The worn spiral staircase is dauntingly steep as you labor northward, throws you sideways as you go east or west, and levels out as you head south, in the direction of the tower’s famous tilt. After 293 dizzying steps to the eighth-story bell chamber, the payoff is a splendid view of rich countryside, mountains and the sea--from a perspective about 13 1/2 feet off center.

“Better to hold the handrail,” Paolo Heiniger warned as he led a reporter where no tourist has trodden since Jan. 7, 1990, after the Italian government hired an international team of engineers to prevent the marble cylinder--completed in 1370--from toppling.

With Heiniger overseeing the $23-million project, the Tuscan icon has stopped its glacial earthward tilt, and the engineers say they have hauled it back just enough to ensure a few more centuries of stable existence. On Saturday, they will return the keys to City Hall, which promises to reopen the tower to climbers by year’s end.

“Now we can have peace of mind,” Mayor Paolo Fontanelli said as work crews tidied up the fenced-off excavation site around the monument in the Plaza of Miracles. “The tower will be with us for many, many years to come.”

When the engineers took over, the 180-foot-tall tower leaned 14 feet 9 inches off center. The tilt had been increasing by about six-hundredths of an inch yearly as soft clay under the southern end gave way at a faster rate than ground under the northern end. The inclination was causing the tower to exert intense pressure on itself at the second story. Engineers feared a collapse.

After five years of near-disastrous trial and error, the engineers found a solution that worked. While steadying the tower temporarily with steel cables overhead and lead ingots at its foundation, they launched a subterranean assault with tubes and drills, gradually removing enough soil from under the higher, northern end to pull back the lean by nearly 16 inches.

That difference is not enough for the human eye to perceive, but it buys valuable time.

“If the tower begins to move at the same rate that it was moving when we became involved, in 1990, about 300 years would pass before it got back to the angle it was then,” explained professor John B. Burland of Imperial College in London, a member of the engineering team.

“By then,” said Heiniger, an Italian who spent much of his career engineering dams and subway tunnels, “new generations of scientists will develop techniques far more sophisticated than ours.”

That is exactly the sort of optimism that prompted Pisa’s civic leaders in the 13th century to turn an embarrassment into a tourist attraction that has been rated as one of the seven wonders of the Middle Ages. The tower was tilting before it was finished, but Pisans forged ahead with construction, realizing that if all other bell towers were straight, a beautiful one that leaned would be a credit to their city.

The tilt reputedly enabled astronomer-physicist Galileo to make his 16th century experiments on gravity and pendular oscillations from the bell tower.

Over the centuries, the lean grew more pronounced, but the 14,500-ton tower survived everything from tourists to earthquakes to the Allied bombardment of Pisa during World War II. Sixteen government commissions studied and fretted over the landmark before the current panel, independent of government ministries, received a mandate from Rome to act.

“When we came in, the movement was accelerating,” Burland said. “We were convinced the tower was very close to falling over.”

Pisans disagreed. Predicting a massive loss of tourism, they kicked up a storm of protest over central government meddling before bowing to Rome’s order to close the tower.

The controversy deepened in 1995, when the engineers tried to connect the tower’s base to a concrete ring but ended up destabilizing the ground below. The tower lurched nearly a tenth of an inch toward the earth in one night, prompting the engineers to abandon plans for a ground anchor.

Rather than decreasing, meanwhile, the number of tourists to Pisa grew--from about 8 million a year in 1990 to about 10 million in 2000, city officials say. Pisans forgot their skepticism and, as the tower stabilized, applauded the work.

One recent afternoon, tourists inquiring about the final stages of the project chatted with engineers through the fence around the tower. “Do you really think you’re going to save it?” one man asked. Tourists took pictures of earth extraction machines. They took pictures of one another, in poses contrived to make it appear that the visitors themselves were helping prop up the tower with their hands.

“The world has developed an enormous interest in the recovery of our sick monument,” said City Hall spokesman Giorgio Piccioni.

Pisans and visitors from all over the globe debated the longevity of the spectacle before them.

“They have performed a miracle. I don’t think the tower will move anymore,” said Giovanni Biondo, who has admired its profile for three decades while selling wooden Pinocchios and little Leaning Towers from a tent-covered stall.

“I’m not so sure,” said John Patterson, a geography professor at the University of Wisconsin in Whitewater. “The ground it is built on is not meant to be stable. Maybe postponing the inevitable is the best they can do.”

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Leaning on Technology

Unstable soil has caused the Leaning Tower of Pisa to tilt southward since the 13th century. Engineers concluded in the early 1990s that the lean was creating dangerous stress on the masonry and posed the threat of collapse. Since 1993 workers have stopped the tilt and pulled the tower back nearly 16 inches--enough, they say, to buy

300 years of stability. Here’s how the tilting occurred and what’s been done about it. It leaned north, then south Work began in 1173 but stopped five years later when a northward tilt was noticed. Engineers overcompensated for the tilt when work resumed in 1272 and the tower began leaning south. It was finished in 1370. By 1817, the tilt had reached 5 degrees. Attempts to repair the lean in 1838, 1934 and during the 1960s and ‘70s only increased it.

Anchor cables

Steel cables with weights were added in 1998 to stabilize the structure while excavation work was done. Each cable was about 335 feet long and able to bear up to 150 tons. (They were never fully tensioned.) All were removed last month.

Masonry stresses

The tower is a hollow cylinder with a covering of marble block walls. Fine wires wrap the second story, the point of maximum stress, to prevent buckling of masonry.

Excavation

Southward tilting of the tower has caused a lifting of the north side of the foun-dation. About 1,760 cubic feet of soil have been extracted by drills from beneath this side, through a row of 41 angled holes, allowing some settling to occur, moving the tower nearly 16 inches upright.

Foundation instability

Compression in the clay layer beneath the south side of the tower has caused it to tilt in that direction, rotating around a point one story above. the ground.

Note: Distances and some engineering elements are conceptual and not to scale.Sources: John B. Burland, Imperial College, London; Paolo Heiniger, manager, Tower of Pisa Project Consortium; Opera Primaziale Pisana.